Transcript Option H: Relativity

Option H: Relativity
H8 Evidence to support general relativity
H.8.1 Outline an experiment for the bending of
electromagnetic waves by a massive object.
H.8.2 Describe gravitational lensing.
H.8.3 Outline an experiment that provides
evidence for gravitational red-shift. The
Pound-Rebka experiment will suffice.
Option H: Relativity
H8 Evidence to support general relativity
Outline an experiment for the bending of
electromagnetic waves by a massive object.
●In 1919, Sir Arthur Eddington conducted the first experiment to determine the
validity of Einstein’s General Theory of
Relativity, published in 1915.
●General relativity’s principle of
equivalence predicts the bending of
light rays in a gravitational field.
●During a total eclipse, the moon blocks
out the sun entirely on certain parts of
the Earth to such an extent that you
can see stars near the disk of the sun.
●In fact, stars that were behind the
sun were expected to be seen,
according to the general theory,
because of the bending of light by its
strong gravitational field.
Option H: Relativity
H8 Evidence to support general relativity
Outline an experiment for the bending of
electromagnetic waves by a massive object.
●Here’s how the experiment worked:
●The sun, moon, Earth and star would all
be lined up for an eclipse.
●The apparent position of the star would be
measured during the eclipse. This position would
be affected by the bending of light by the sun.
●The true position of the star would be
determined 6 months after the apparent position
of the star was recorded. Why 6 months?
Apparent
star
Earth
/moon
Sun
Actual
star
Option H: Relativity
H8 Evidence to support general relativity
Outline an experiment for the bending of
electromagnetic waves by a massive object.
●Relativity predicted a deflection of 1.75 arc
seconds for starlight passing close to the edge
of the sun.
●Although Eddington’s results were in agreement
with relativity, his uncertainty was comparable
to the measurement itself.
●Furthermore, his results were disputed by
another team doing the same thing in Brazil.
FYI
The Eddington-Einstein collaboration continued
through the First World War, even though the two
scientists were on opposite sides.
The results of Eddington’s observations have
sometimes been criticized as a “self-fulfilling”
desire to prove general relativity correct.
Option H: Relativity
H8 Evidence to support general relativity
Describe gravitational lensing.
●If a sufficiently massive
object is between an observer
and a distant object, because
of the bending of the light by
gravity, the mass acts like a
lens.
●A gravitational lens will
present to the observer numerous
images of the same distant object.
EXAMPLE:
Here are images of
so-called Einstein
rings (gravitational lens
images).
This is an animation of gravitational lensing.
●The dark object doing the lensing is a massive
black hole between us and the band of stars.
●The band of stars is a galaxy on edge, farther
away than the black hole.
●Note the Einstein rings.
Option H: Relativity
H8 Evidence to support general relativity
22.6 m
Outline an experiment that provides evidence for
gravitational red-shift.
●We have already done a sample problem
modeled on the Pound-Rebka experiment.
●This experiment, conducted in the
Jefferson Laboratory at Harvard in
1959, verified the
gravitational red
shift by detecting the
change in frequency of
gamma rays emitted by
57Fe.
The “Tower”